Antimutagenic activity of polymethoxyflavonoids from Citrus aurantium

The methanol extract from Citrus aurantium showed a suppressive effect on u mu gene expression of SOS response in Salmonella typhimurium TA1535/pSK1002 against the mutagen 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide (furylfurami de). The methanol extract from C. aurantium was successively re-extracted w ith hexane, dichloromethane, butanol, and water. A dichloromethane fraction showed a suppressive effect. The suppressive compounds in the dichlorometh ane fraction were isolated by SiO2 column chromatography and identified as tetra-O-methylscutellarein (1), sinensetin (2), and nobiletin (3) by EI-MS and H-1- and C-13 NMR spectroscopy. These compounds suppressed the furylfur amide-induced SOS response in the umu test. Gene expression was suppressed 67%, 45%, and 25% at a concentration of 0.6 mu mol/mL, respectively. The ID 50 value (50% inhibition dose) of compound 1 was 0.19 mu mol/mL. These comp ounds were assayed with other mutagens, 3-amino-1,4-dimethyl-5H-pyrido[4,3- b]indole (Trp-P-1), which requires liver metabolizing enzymes, activated Tr p-P-1, and UV irradiation. These compounds showed of all mutagen-induced SO S response in the umu test. In addition, compounds 1-3 exhibited antimutage nic activity in the S. typhimurium TA100 Ames test.